首页|Early Triassic Silicic Volcanics of South China:Petrogenesis and Constraints on the Geodynamic Evolution of the Paleo-Tethys Ocean Region
Early Triassic Silicic Volcanics of South China:Petrogenesis and Constraints on the Geodynamic Evolution of the Paleo-Tethys Ocean Region
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The only occurrence of Lower Triassic silicic volcanic rocks within the South China Block is in the Qinzhou Bay area of Guangxi Province.LA-ICP-MS zircon U-Pb dating reveals that volcanic rocks of the Beisi and Banba formations formed between 248.8±1.6 and 246.5±1.3 Ma,coeval with peraluminous granites of the Qinzhou Bay Granitic Complex.The studied rhyolites and dacites are characterized by high SiO2,K2O,and Al2O3,and low MgO,CaO,and P2O5 contents and are classified as high-K calc-alkaline S-type rocks,with A/CNK=0.98-1.19.The volcanic rocks are depleted in high field strength elements,e.g.,Nb,Ta,Ti,and P,and enriched in large ion lithophile elements,e.g.,Rb,K,Sr,and Ba.Although the analyzed volcanic rocks have extremely enriched zircon Hf isotopic compositions(εHf(t)=-29.1 to-6.9),source discrimination indicators and high calculated Ti-in-zircon temperatures(798-835℃)reveal that magma derived from enriched lithospheric mantle not only provided a heat source for anatectic melting of the metasedimentary protoliths but was also an endmember component of the S-type silicic magma.The studied early Triassic volcanics are inferred to have formed immediately before closure of the Paleo-Tethys Ocean in this region,as the associated subduction would have generated an extensional setting in which the mantle-derived upwelling and volcanic activity occurred.
WANG Yabo、LIU Lei、ZHAO Zengxia、LIU Xijun、HUANG Wenmin
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Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,College of Earth Sciences,Guilin University of Technology,Guilin,Guangxi 541004,China
Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources,Guilin University of Technology,Guilin,Guangxi 541004,China
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